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  1. elimMaybe :: forall a (p :: Maybe a ~> Type) (s :: Maybe a) . Sing s -> Apply p ('Nothing :: Maybe a) -> (forall (f0 :: a) . () => Sing f0 -> Apply p ('Just f0)) -> Apply p s

    eliminators Data.Eliminator

    No documentation available.

  2. EMaybe :: ElmDatatype -> ElmPrimitive

    elm-export Elm

    No documentation available.

  3. eitherMaybe :: Either () a -> Maybe a

    errors-ext Control.Error.Extensions

    Converts Either to Maybe. Specialization of either. 

    maybeEither . eitherMaybe = id

  4. productMaybeWith :: (a -> b -> Maybe c) -> [[a]] -> [[b]] -> [[c]]

    extrapolate Test.Extrapolate

    Take the product of lists of tiers by a function returning a Maybe value discarding Nothing values.

  5. productMaybeWith :: (a -> b -> Maybe c) -> [[a]] -> [[b]] -> [[c]]

    extrapolate Test.Extrapolate.Core

    Take the product of lists of tiers by a function returning a Maybe value discarding Nothing values.

  6. eitherToMaybe :: Either e a -> Maybe a

    from-sum Control.FromSum

    Convert an Either to a Maybe. A Right value becomes Just. 

    >>> eitherToMaybe $ Right 3
Just 3
    A Left value becomes Nothing. 
    >>> eitherToMaybe $ Left "bye"
Nothing

  7. fromMaybe :: a -> Maybe a -> a

    from-sum Control.FromSum

    The fromMaybe function takes a default value and a Maybe value. If the Maybe is Nothing, it returns the default value; otherwise, it returns the value contained in the Maybe.

    Examples

    Basic usage: 
    >>> fromMaybe "" (Just "Hello, World!")
"Hello, World!"

    >>> fromMaybe "" Nothing
""
    Read an integer from a string using readMaybe. If we fail to parse an integer, we want to return 0 by default: 
    >>> import GHC.Internal.Text.Read ( readMaybe )

>>> fromMaybe 0 (readMaybe "5")
5

>>> fromMaybe 0 (readMaybe "")
0

  8. fromMaybeExceptT :: forall (m :: Type -> Type) x a . Monad m => x -> Maybe a -> ExceptT x m a

    from-sum Control.FromSum

    Lift a Maybe to an ExceptT with a default value for the case when the Maybe is Nothing. If the Maybe is Just, then just return the value like normal: 

    >>> let justVal = Just True :: Maybe Bool

>>> fromMaybeExceptT 5 justVal :: ExceptT Int Identity Bool
ExceptT (Identity (Right True))
    If the Maybe is Nothing, then use the default value as the error value: 
    >>> let nothingVal = Nothing :: Maybe Bool

>>> fromMaybeExceptT 5 nothingVal :: ExceptT Int Identity Bool
ExceptT (Identity (Left 5))

  9. fromMaybeM :: Applicative m => m a -> Maybe a -> m a

    from-sum Control.FromSum

    A monadic version of fromMaybe. 

    fromMaybeM nothingAction === maybe nothingAction pure

    >>> fromMaybeM [] $ Just 5
[5]

>>> fromMaybeM [] Nothing
[]

  10. fromMaybeMExceptT :: Monad m => x -> m (Maybe a) -> ExceptT x m a

    from-sum Control.FromSum

    Similar to fromMaybeExceptT except the Maybe value is lifted in a Monad. 

    >>> let identityNothing = Identity Nothing :: Identity (Maybe Bool)

>>> fromMaybeMExceptT 5 identityNothing :: ExceptT Int Identity Bool
ExceptT (Identity (Left 5))

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